1. Field of the Invention
The present invention relates to a fastening portion for a steering apparatus which has a non-circular hole for fastening a non-circular shaft portion at an end of a rotational shaft in order to transmit a rotational torque of a steering apparatus and more particularly to a fastening portion of an extension shaft which has a non-circular hole for fastening a non-circular shaft portion at an end of a pinion shaft which is brought into mesh engagement with a rack of a steering gear and a manufacturing method for the same.
2. Description of Related Art
As a fastening portion for a steering apparatus like one described above, as is described in Japanese Utility Model Unexamined Publication JP-UM-A-55-38024, there is a universal joint which includes a fastening portion for fastening a non-circular shaft portion which is defined by two parallel planes. In addition, as a method for fastening portion for a steering apparatus, there is a method, described in Japanese Patent Examined Publication JP-B-6-58124, for producing a universal joint.
FIG. 6 is a process diagram which shows a manufacturing method for a conventional extension shaft in which a fastening portion is formed by broaching. As shown in FIGS. 11A, 11B, 11C, in a conventional extension shaft 8 in which a fastening portion is formed by broaching, in order to broach a non-circular hole in a fastening portion 81, the fastening portion 81 is formed separately from a shaft portion 82.
The non-circular hole 83, which passes through the fastening portion 81 in an axial direction (in a horizontal direction in FIG. 11B) of the fastening portion 81 at an axial center thereof, is broached. Thereafter, as shown in FIG. 12, a small diameter shaft portion 821 at a left end of the shaft portion 82 is fitted in a circular hole 811 at a right end of the fastening portion 81, and the fastening portion 81 and the shaft portion 82 are joined together integrally by means of welding.
Consequently, the extension shaft 8 is thermally deformed by heat generated at the time of welding, whereby the dimension accuracy is reduced, and the number of working processes is increased, leading to a problem that the production costs are increased.
FIGS. 13A, 13B are process diagrams which shows a manufacturing method for a conventional extension shaft in which a fastening portion is formed by forging. As shown in FIGS. 13A, 13B, in an extension shaft 9 in which a fastening portion is formed by forging, a fastening portion 91 and a shaft portion 92 are forged integrally, and a non-circular hole 93 in the fastening portion 91 is also formed by forging at the same time that the fastening portion 91 is forged.
When the non-circular hole 93 is forged at the same time that the fastening portion 91 is forged, since an eccentric load is applied to the fastening portion 91 while the non-circular hole 93 is being forged, the fastening portion 91 collapses. In order to bear effectively the eccentric load to prevent the collapse of the fastening portion 91, a padding 96, which is formed into a symmetrical shape with a clamping portion 95 having a slot 94, is added to an exterior of the fastening portion 91 on an opposite side to a side where the clamping portion 95 is provided.
Consequently, this has resulted in a problem that the weight of the extension shaft 9 is increased and a space necessary for the attachment of the extension shaft 9 to a vehicle body is increased.